1. Field of the Invention
The present invention relates to diaphragms for speakers and manufacturing methods therefor.
This application claims priority on Japanese Patent Application No. 2006-185712, the content of which is incorporated herein by reference.
2. Description of the Related Art
According to the conventionally-known manufacturing methods, thin wooden boards are subjected to press working or molding so as to produce diaphragms for use in speakers. Japanese Unexamined Patent Application Publication No. H06-178386 teaches that a single sheet of a thin wooden board is subjected to press working so as to produce a diaphragm, or plural sheets of thin wooden boards are laminated together and are then subjected to press working so as to produce a diaphragm. It also teaches that a thin wooden board is formed in a cone shape in advance and is then subjected to press working so as to produce a diaphragm.
Japanese Unexamined Patent Application Publication No. 2004-254013 teaches that a thin wooden board having a V-shaped cutout is prepared in advance; the thin wooden board is softened by way of the addition of water thereto; opposite sides along the V-shaped cutout are adhered together by way of primary pressing; the thin wooden board after the primary pressing is impregnated with a thermosetting resin; then, the thin wooden board impregnated with the thermosetting resin is subjected to secondary pressing so as to produce a diaphragm.
In general, thin wooden boards are easily broken or split along the grains thereof during press working or molding. For this reason, in the manufacturing method taught in Japanese Unexamined Patent Application Publication No. H06-178386, the thin wooden board is subjected to steaming prior to molding, or it is subjected to boiling using an alkali solution prior to molding, thus making the thin wooden board have flexibility, whereby it is possible to control the occurrence of cracks during the molding. It is necessary that the diaphragm formed by way of press working be subjected to treatment in order to improve the durability thereof. Therefore, a coat of urethane varnish is applied to the thin wooden board after press working. However, the aforementioned manufacturing method is complex because it needs various processes before or after the press working.
The manufacturing method taught in Japanese Unexamined Patent Application Publication No. 2004-254013 is also complex because it performs press working twice. Since the opposite sides of the V-shaped cutout of the thin wooden board are adhered together, directions of the grains greatly change at the boundary of the adhered portion. This causes irregularity in terms of directions of the grains in the diaphragm, which in turn degrades the acoustic characteristics of the diaphragm or which in turn causes cracks in the diaphragm along specific directions. In addition, the adhered portion is slightly increased in thickness compared with the thickness of the other portion of the diaphragm. That is, the diaphragm suffers from irregularity in terms of the thickness, which in turn degrades the acoustic characteristics thereof.